1. Field
Exemplary embodiments of the present invention relate to a latch circuit.
2. Description of the Related Art
A latch circuit temporarily stores data. Latch circuits are frequently used in all kinds of semiconductor devices. As the degree of integration of a semiconductor device increases, the capacitance value of the storage node of a latch circuit is reduced. This results in an increase in soft errors, where the data stored in the storage node of the latch circuit changes. Soft errors are a phenomenon in which data stored in a latch circuit is altered by a cosmic ray, such as an alpha particle.
FIG. 1 is a diagram illustrating a conventional latch circuit. FIG. 1 shows how a soft error occurs in the conventional latch circuit.
Referring to FIG. 1, the latch circuit includes an inverter INV1 having an NMOS transistor T1 and a PMOS transistor T2 and an inverter INV2 having an NMOS transistor T3 and a PMOS transistor T4. Input/output terminals of the inverters INV1 and INV2 are connected to each other, so that data is retained.
When data having a logic high level ‘H’ is stored in a node B and data having a logic low level ‘L’ is stored in a node A, the PMOS transistor T2 and the NMOS transistor T3 are turned on and the NMOS transistor T1 and the PMOS transistor T4 are turned off.
On the other hand, when data having a logic low level is stored in the node B and data having a logic high level ‘H’ is stored in the node A, the PMOS transistor T2 and the NMOS transistor T3 are turned off and the NMOS transistor T1 and the PMOS transistor T4 are turned on.
The node A may be an input node of the latch circuit and the node B may be an output node of the latch circuit. By a cross-coupled structure, the latch circuit retains data.
In general, soft errors occur when current flows through a turned-off NMOS transistor, which is induced by a cosmic ray. IN contrast, a cosmic ray rarely causes current to flow through a turned-off PMOS transistor. For example, when data having a logic low level ‘L’ is stored in the node A, due to current flowing through the NMOS transistor T1 caused by a cosmic ray, the voltage of the node B is changed from ‘H’ to ‘L’ and the voltage of node A is changed from ‘L’ to ‘H’. That is, data stored in the latch circuit is lost, and a soft error occurs.